Preparation of hydrates of 2cao.3b2o3



United States Patent Ofi ice 3,337,292 Patented Aug. 22, 1967 ABSTRACT OF THE DISCLOSURE Hydrates of 2Ca0-3B O are synthesized by reacting Ca(IO with a borax solution, or CaCl with a (NH4)2B10O16'8H2O solution, to form higher hydrates. These higher hydrates may be converted to synthetic colemanite by reaction with borax solution.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This is a division of U.S. patent application Ser. No. 268,845 filed Mar. 28, 1963 for Synthetic Ferroelectric Colemanite and Its Strontium Isomorph.

The present invention relates to synthetic ferroelectric colemanite and more particularly to the preparation of hydrates of 2CaO-3B O Colemanite is a mineral calcium borate pentahydrate found in relative abundance in conjunction with other borate minerals. At temperatures generally below 2 C. to 7 C. crystalline colemanite becomes ferroelectric and remains ferroelectric at least to (-l80 0). Colemanite is a mechanically, electrically, and chemically stable ferroelectric material. It shows none of the polarization fatigue effects associated with barium titanate nor is it subject to deliquescence at temperatures below +50 C. as some other water soluble ferroelectric materials. Mineral colemanite contains many impurities. It is dif ficult, therefore, to determine the dependence of the desirable electrical properties upon the impurity content of a crystal. For switching applications, it is desirable to keep the transition temperature, i.e., the Curie temperature, above +25 C. in order that no refrigeration be required for a computer memory device employing colemanite crystals. For its use as a dielectric bolometer or pyroelectric detector, it is desirable to control the Curie point by additive impurities so that the maximum change in polarization with temperature should occur at some predetermined temperature. Therefore, mineral colemanite because of its inhomogeneity, is not suited for these aforementioned applications and that the synthesis of the pure compound is required.

It is an object of the invention therefore to provide the synthesis of 2CaO'3B O -7H O.

It is another object of the invention to provide the synthesis of 2CaO 3B O 9H O.

It is a further object of the invention to provide for the synthesis of 2CaO-3B O l3H O.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description.

The publication, Ferroelectric and Pyroelectric Properties of Mineral and Synthetic Colemanite by H. H. Wieder, A. R. Clawson and C. R. Parkerson, Journal of Applied Physics, 33, 1720 (1962), describes in detail the results obtained on synthetic colemanite and compares the dielectric and pyroelectric properties of the synthetic compound with the impure mineral.

Colemanite may be synthesized by a two-step reaction. The first step consists of the synthesis of inyoite (2CaO- 3B O -13H O) synthetic (2CaO'3B O -9H O), or meyerhoflerite (2Ca0- 3B O 7H O) For these reactions see Reactions 1, 2, and 3 of the Table of Reactions which follows. These higher hydrates may be converted to colemanite (2CaO-3B O -5H by reaction with borax solution. For an example of. this conversion reaction see Reaction No. 4. Colemanite can also be synthesized by the preparation of gowerite (CaO-3B O -5H O) or nobleite (CaO-3B O -4H O) as given in Reactions 5 and 7. Reaction of either of these two compounds with borax solution as given in Reactions 6 and 8 will produce colemanite.

TABLE OF REACTIONS Reactant I Reactant II Water, Reaction No. Amount Chemical Formula Weight Chemical Formula Weight (grams) (grams) (grams) Na2B4O1-10H2O 1. 67 l. 94 100 Na2B407-10HaO" 1.67 1.94 100 (N114) zB nOm-8Hz l. 00 9.012 0. 43 100 N8.2B407-10H2 1. 71 2CaO-3BzO3-7Hg (200 mesh) 1.00 100 113B 03 40-0 Ca(C2HsO2)2 20.0 100 NazB4O7-10H10 2. 24 CaO-3B2O3-5H2O (Gowerite) 1. 25 150 H 130. 5.29 2CaO-3BzOa-7Hz0 1.85 100 Na2'B4O7-1OH1O 2. 24 CaO-3B 208'4H20 (Nobleite) 1. 25 150 (N'H4)zB1uOw.-8HgO 16.0 S!(N0a)2 7.10 800 Na2B4O -10H O 2. 24 1. 25 150 Nfi,2B407-10HzO 7-60 4. 20 200 Naz'B4O7-10HzO 4- 1. 50 150 H3 3 3. 00 1. 50 150 Na2B401-10HiO 2. 24 l. 25 150 NazB4O1-10H2O 4. 02 2. NazB 401-10H20 2. 24 SIC-3320a 4H2O (Compound V) 1. 25 150 NEzB40r10H20. 4- 02 S1(I0a) 2 H2O 2. 55 150 NagB40izO-10H 11. 44 SIClz-fiHzO'. 8. 00 200 TABLE OF REACTloNs continued Reactant III or Seed Material (if required) Time Tempera- Reaction No. (days) ture, 0. Product Chemical Formula Weight (grams) 34 30 Inyoite (208.0-313203431302) 65 Meyerhofferite (2CaO-3BzO3-7Hz0) 41 30 Synthetic (20210-313 2Os-9Hz0) 2CaO'3B203-5HzO (200 mesh) 0.10 35 65 Colemanite (2CaO-3BzO;-5Hz0) 1 35 Gowerite (CELO-3BzO3-5HzO) 203-O-3B203-5H20 (200 mesh) 0. 65 Colemanite (2CaO-3B20s-5H20, 7- 8 85 Nobleite (CaO-BBzOsAHzO) 8 ZCaO3B2O3-5HQO (200 mesh) 0.10 19 65 Colemanite (2O210-3B2O3-5H20) 9. 7 Compound III (SlO-3'B2Os-4II2O) 10--. 13 65 Compound I (2STO-3B20s-5H20) 11 NaOH 3.2, 7 25 Compound VI (SrO-BrOa-4H2O) 12---- 27 65 Compound I (2SrO-3BzOz-5H2O) 13 13 65 Compound IV (SrO'3BzO3-4HzO) 14- 8 65 Compound I (2SrO'3BQO3-5HZO) 15--- NaOH- 0.80 5 65 Compound V (SIO-3B2Os-4H2O) 16- 27 65 Compound I (2SIO-3BzO -5H2O) l7 14; 65 Compound I (2SIO-3BzOs-5H2O) 18.; 36 80 Compound I (2SrO-3BzOa-5H2O) It was suspected at an earlier date (H. H. Wieder, J. Appl. Phys. 30, 1010 (1959)) that the onset of ferroelectricity in colemanite may be strongly influenced by the presence of strontium replacing calcium substitutionally in the crystal-lattice of colemanite.

Partial substitutes of strontium for calcium in colemanite is achieved by preparing the higher hydrate in the presence of the desired strontium ion impurity in the form of a highly ionized strontium compound such as SrCl Sr(NO) etc. or a partially ionized compound such as Sr(IO -H O. The higher hydrate is then converted to colemanite with borax solution as previously described. If a higher percentage of replacement is desired, strontium ion may be added to this conversion reaction also.

The discrepancies between various authors as to the exact Curie temperature of colemanite ranging between 0 C. and 7 C. were suspected as due primarily to the variable strontium content of colemanite, i.e., that mineral colemanite is thus a solid solution of calciumstrontium borate pentahydrate. It was proposed, the-refore, to produce a synthetic colemanite containing a large amount of strontium instead of calcium. The method is outlined below:

i The first step consisted of the preparation of a specimen as follows (for example):

Reactants:

H O ml 800 Ammonium pentaborate gm 16.0 SI'(NO3)2H2O gm The ammonium pentaborate was dissolved in 700 ml. H O by heating to approximately 85* C. The

was dissolved in 100 ml. H O at approximately 85 C. The 100 ml. of Sr(NO -H O solution was added to the 700 ml. of APB while hot, a few crystal seeds of synthetic meyerhofferite was added, and the container was sealed and allowed to cool to room temperature with continuous agitation. Continuous agitation was maintained for a period of three weeks. The reaction products were then used for preparing the strontium synthetic equivalent of colemanite by the following procedure and using the indicated constituents:

Grams Borax 2.24 The specimen preparation described above 1.25 H O 150 The above was heated and sealed at 70 C. and maintained at that temperature for 13 days with continuous agitation by means of a shaker table. A second sample was prepared in an identical manner except that the reaction was allowed to proceed for 35 days. The resultant crystallites are microscopic in size. The Debye- Sherer X-ray pattern, the dielectric properties and the pyroelectric properties were measured. The X-ray diff-raction powder pattern of the strontium isomorph of colemanite was compared with the powder pattern of natural colemanite. The X-ray powder diffraction pattern of the Sr isomorph bore a striking similarity to that of natural colemanite.

In order to test the dielectric and pyroelectric properties pressed powder pellets were prepared in accordance with the description in the publication by Wieder, Clawson, and Parkerson aforementioned. The strontium isomorph of colemanite obeys a Curie-Weiss relation since the capacitance which may be considered as proportional to the electrical susceptibility has the typical dependence of ferroelectrics in the vicinity of their Curie temperatures. The Curie temperature of the strontium isomorph is +30 C. Subsequent measurements performed on other samples established the Curie temperature to be between +30 and +35 C. This is also supported by pyroelectric data which illustrates the magnitude of the pyroelectric signal as a function of temperature. The experimental method for obtaining the pyroelectric response is also described in the publication by Wieder, Clawson, and Parkerson.

The data presented here for the colemanite strontium isomorph represent a shift of the Curie temperature from -35 C. for the pure synthetic colemanite to +35 C. The advantages of the addition of strontium and its substitution in the crystal lattice of colemanite represent a method for controlling and tailoring the properties of this material for obtaining a peak response of a pyroelectric detector at some predetermined temperature between +35 C. and 35 C. Also, the operation of ferroelectric memory elements from the strontium isomorph may be used at or near room temperature.

The strontium isomorph, Compound I of colemanite replacement of calcium by strontium) can be synthesized by several reactions. The fol- 5 lowing related strontium borate hydrates may also be prepared as given in Table of Reactions:

Compound III (SrO-3B O -4H O), Reaction No. 9.

Compound IV (SrO-3B O -4H Tunellite, Reaction Compound V (SrO'B O -4H O), Reaction No. 15.

Compound VI (SrO-B O -4H O), Reaction No. 11.

tion of borax with a partially ionied strontium compound 15 such as Sr(IO -H O (see Reaction 17). Direct reaction of borax with a highly ionized strontium compound such as SrCl -6H O or Sr(NO produces Compound I (see Reaction 18).

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. The preparation of the higher hydrate 2030 3B O3 y,

6 (a) reacting 2 parts by weight of C-a(IO with 100 parts by Weight of approximately 1.7% borax solution at 30 C. for approximately 34 days, (b) filtering, washing, and drying the crystalline reaction product 2CaO 3B O 13H O. 2. The preparation of the higher hydrate (a) reacting 1 part by weight of CaCl with 200 parts by Weight of approximately 1% (NH B O -8H O solution at 30 C. for approximately 41 days, (b) filtering, washing, and drying the crystalline reaction product 2CaO-3B O -9H O.

References Cited 25 Memo No. 42-31, June 1959, pages 1-8.

OSCAR R. VERTIZ, Primary Examiner.

H. T. CARTER, Assistant Examiner. 

1. THE PREPARATION OF THE HIGHER HYDRATE
 2. THE PREPARATION OF THE HIGHER HYDRATE 